With the evolution of semiconductor packaging technology, semiconductor devices have developed different types of packaging. Among which, ball grid array (BGA), such as PBGA, EBGA, FCBGA, etc., is an advanced semiconductor packaging technology, characterized by the use of a package substrate to accommodate a semiconductor element, with solder balls arranged in a grid array on a back side of the package substrate. The entire packaging unit is electrically connected to external electronic device(s) through the soldering of these solder balls, so that the same area of the unit on the carrier is able to accommodate more input/output (I/O) connections in order to meet the need for high integration of the semiconductor chips.
Furthermore, in order to be in line with the development in the directions of compact, light, versatile, high-speed and high-frequency semiconductor packages, the development of chips has been focused on areas of fine lines and small aperture.
As shown in FIG. 1, a traditional flip-chip semiconductor package 1 includes a semiconductor chip 13 disposed on a packaging substrate 10. More specifically, the packaging substrate 10 includes a plurality of electrical contact pads 11, and the packaging substrate 10 and the electrical contact pads 11 are covered with an insulating protection layer 12. The insulating protection layer 12 has a plurality of openings 120 for exposing the corresponding electrical contact pads 11, such that a plurality of solder bumps 14 are joined with the electrical contact pads 11 in the various openings 120, allowing reflow of the various solder bumps 14 in order to connect with the semiconductor chip 13.
However, in subsequent heating process, the volume of the solder bumps 14 will increase by about 30 to 50%, such that some of the soldering materials 140 of the solder bumps 14 may seep into the space between the insulating protection layer 12 and the electrical contact pads 11 or between the insulating protection layer 12 and the packaging substrate 10, resulting in solder extrusion. When the bump pitch between two adjacent electrical contact pads 11 is small, the phenomenon of bridging tends to happen, causing short circuits and decreasing product yield.
In order to avoid the above phenomenon of bridging caused by solder extrusion, a metal layer can be formed above the electrical contact pads 11 to stop the permeation of the soldering materials 140. More specifically, as shown in FIG. 1′, a packaging substrate 10 includes a base 10a and a circuit structure 10b disposed on the base 10a, wherein electrical contact pads 11 and a plurality of conductive traces 100 are disposed on the circuit structure 10b, and a metal layer 15 is formed on the electrical contact pads 11 in order to bond the solder bumps 14, wherein the metal layer 15 includes Ni/Pd/Au. The metal layer 15 prevents the soldering materials from seeping between the insulating protection layer 12 and the electrical contact pads 11 or between the insulating protection layer 12 and the packaging substrate 10 during reflow of the solder bumps 14.
However, the method of using the metal layer 15 to cut off the soldering materials will inevitably increase the manufacturing cost of the packaging substrate 10 by 10% to 25%. This is not economical.
Therefore, there is a need for a solution that addresses the aforementioned issues in the prior art.